Resolution and identification of elemental compositions for more than 3000crude acids in heavy petroleum by negative-ion microelectrospray high-field Fourier transform ion cyclotron resonance mass spectrometry

Although crude acids are minor constituents in petroleum, they have signifi cant implications for crude oil geochemistry, corrosion, and commerce. We h ave previously demonstrated that a single positive-ion electrospray ionizat ion (ESI) high-field Fourier transform ion cyclotron resonance mass spectro metry (FT-ICR MS) experiment can resolve and identify 3000 chemically diffe rent elemental compositions of bases (basic nitrogen compounds) in a crude oil. Here, we show that negative-ion ESI high-field FT-ICR MS can selective ly ionize and identify naphthenic acids without interference from the hydro carbon background. When combined with prechromatographic separation, ESI FT -ICR MS reveals an even more detailed acid composition. An average mass res olving power, m/Deltam(50%) greater than or equal to 80 000 (Deltam(50%) is mass spectral peak full width at half-maximum peak height) across a wide m ass range (200 < m/z < 1000), distinguishes as many as 15 distinct chemical formulas within a 0.26 Da mass window. Collectively, more than 3000 chemic ally different elemental compositions containing O-2, O-3, O-4, and O2S, O3 S, and O4S were determined in a South American heavy crude. Our data indica tes that the crude acids consist of a mixture of structures ranging from C- 15-C-55 with cyclic (1-6 rings) and aromatic (1-3 ring) structures. The aci d composition appears to be simpler than that of the corresponding hydrocar bon analogues.